Conventionally, various navigation devices have been developed in view of prevention of collision between ships and safety of life. For example, a radar device having a TT (Target Tracking) function has been known as such a navigation device. Here, simply put, the TT function is for detecting a position and a velocity vector of a target object that exists around a ship concerned, based on a transition of a radar image obtained previously. JP2009-122063A discloses a configuration including two radar devices having the TT function.
The two radar devices disclosed in JP2009-122063A form a configuration in which one of the radar devices displays information acquired by the other radar device. For example, when the radar device cannot appropriately acquire TT information due to influence of clutter, an operator selects a target from a radar image displayed by the other radar device and, thus, the corresponding target can be displayed by the radar device.
However, with the configuration of JP2009-122063A, the target is displayed in different forms between the two radar devices. Therefore, it has not been able to instantly determine the target displayed by the other radar device which corresponds to the target that is not displayed appropriately by the radar device.